Thermally Activated Well Perforating Safety System

ABSTRACT

An explosives safety system includes an explosive component, a blocking member displaceable to selectively permit and prevent detonation of the explosive component, and a thermal actuator responsive to temperature change and configured to displace the member in response to the temperature change. Another explosives safety system includes a thermal actuator with a material having a volume variable in response to the temperature change, and detonation of the explosive component being selectively permitted and prevented by the actuator when the material volume changes. A method of preventing undesired detonation of an explosive component includes the steps of: providing a material having a volume variable in response to a change in a temperature; positioning the material and the explosive component in a well, thereby increasing the material temperature; increasing the material volume in response to the increasing temperature; and permitting detonation of the explosive component in response to the increasing volume.

BACKGROUND

The present invention relates generally to equipment used and operationsconducted in conjunction with a subterranean well and, in an embodimentdescribed herein, more particularly provides a thermally activatedexplosives safety system.

In well perforating operations, it is vitally important to preventundesired detonations of explosive components. Injury or even death ofpersonnel can result from untimely detonations, as well as damage to thewell, surface equipment and other property.

Various safety systems have been used in the past, but these have notbeen entirely successful. Some safety systems rely on pressure toprovide an actuating force, with the pressure being present onlydownhole. Other systems rely on temperature downhole to melt asubstance, such as a eutectic material, thereby permitting detonation ofan explosive component.

Unfortunately, in some such systems the substance cannot be reformed or“un-melted” in the event that the explosive component has to beretrieved from the well, so that the substance again prevents detonationof the explosive component. Those systems which do permit reforming ofthe melted substance have a relatively large operating envelope. Thisre-arming of the safety system is important if, for example, aperforating gun or firing head mis-fires downhole and has to beretrieved to the surface with undetonated explosive components therein.

Therefore, it may be seen that improvements are needed in the art ofthermally activated explosives safety systems.

SUMMARY

In carrying out the principles of the present invention, explosivessafety systems and associated methods are provided which solve at leastone problem in the art. One example is described below in which athermal actuator is used to alternately permit and prevent detonation ofan explosive component. Another example is described below in which amaterial has a volume which varies in response to a temperature change,and the variable material volume is used to alternately permit andprevent detonation of an explosive component.

In one aspect of the invention, a thermally activated explosives safetysystem is provided. The system includes an explosive component and ablocking member displaceable to selectively permit and preventdetonation of the explosive component. A thermal actuator of the systemis responsive to temperature change. The actuator is configured todisplace the blocking member in response to the temperature change.

In another aspect of the invention, a thermally activated explosivessafety system includes a thermal actuator responsive to temperaturechange, the actuator including a material having a volume which isvariable in response to the temperature change. Detonation of theexplosive component is selectively permitted and prevented by theactuator when the material volume changes.

In yet another aspect of the invention, a method of preventing undesireddetonation of an explosive component includes the steps of: providing amaterial having a volume which is variable in response to a change in atemperature of the material; positioning the material and the explosivecomponent in a subterranean well, thereby increasing the temperature ofthe material; increasing the volume of the material in response to thetemperature increasing step; and permitting detonation of the explosivecomponent in response to the volume increasing step.

These and other features, advantages, benefits and objects of thepresent invention will become apparent to one of ordinary skill in theart upon careful consideration of the detailed description ofrepresentative embodiments of the invention hereinbelow and theaccompanying drawings, in which similar elements are indicated in thevarious figures using the same reference numbers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic partially cross-sectional view of a well systemand associated method embodying principles of the present invention;

FIG. 2 is an enlarged scale schematic cross-sectional view through athermally activated explosives safety system in the well system of FIG.1;

FIG. 3 is a schematic cross-sectional view of a first alternateconfiguration of the explosives safety system;

FIG. 4 is a schematic cross-sectional view of the first alternateconfiguration of the explosives safety system, taken along line 4-4 ofFIG. 3, wherein detonation of an explosive component is prevented;

FIG. 5 is a schematic cross-sectional view of the first alternateconstruction of the explosives safety system, wherein detonation of theexplosive component is permitted;

FIG. 6 is a schematic cross-sectional view of a second alternateconfiguration of the explosives safety system, wherein detonation of anexplosive component is prevented;

FIG. 7 is a schematic cross-sectional view of the second alternateconfiguration of the explosives safety system, wherein detonation of theexplosive component is permitted;

FIG. 8 is a schematic cross-sectional view of a third alternateconfiguration of the explosives safety system;

FIG. 9 is a schematic cross-sectional view of a fourth alternateconfiguration of the explosives safety system;

FIG. 10 is a schematic cross-sectional view of a fifth alternateconfiguration of the explosives safety system, wherein detonation of anexplosive component is prevented;

FIG. 11 is a schematic cross-sectional view of the fifth alternateconfiguration of the explosives safety system, wherein detonation of theexplosive component is permitted;

FIGS. 12 & 13 are schematic side elevational views of multiple thermalactuators usable in the various configurations of the explosives safetysystem, the actuators being depicted in a retracted condition in FIG.12, and in an extended condition in FIG. 13;

FIG. 14 is a schematic cross-sectional view of a sixth alternateconfiguration of the explosives safety system;

FIG. 15 is a schematic cross-sectional view of a seventh alternateconfiguration of the explosives safety system;

FIG. 16 is a schematic cross-sectional view of a eighth alternateconfiguration of the explosives safety system, wherein detonation of anexplosive component is prevented;

FIG. 17 is a schematic cross-sectional view of the eighth alternateconfiguration of the explosives safety system, wherein detonation of theexplosive component is permitted;

FIG. 18 is a schematic cross-sectional view of a ninth alternateconfiguration of the explosives safety system;

FIG. 19 is a schematic cross-sectional view of a tenth alternateconfiguration of the explosives safety system;

FIG. 20 is a schematic cross-sectional view of an eleventh alternateconfiguration of the explosives safety system;

FIG. 21 is a schematic cross-sectional view of a twelfth alternateconfiguration of the explosives safety system;

FIG. 22 is a schematic cross-sectional view of a thirteenth alternateconfiguration of the explosives safety system;

FIG. 23 is a schematic cross-sectional view of a fourteenth alternateconfiguration of the explosives safety system; and

FIG. 24 is a schematic cross-sectional view of a fifteenth alternateconfiguration of the explosives safety system.

DETAILED DESCRIPTION

It is to be understood that the various embodiments of the presentinvention described herein may be utilized in various orientations, suchas inclined, inverted, horizontal, vertical, etc., and in variousconfigurations, without departing from the principles of the presentinvention. The embodiments are described merely as examples of usefulapplications of the principles of the invention, which is not limited toany specific details of these embodiments.

In the following description of the representative embodiments of theinvention, directional terms, such as “above”, “below”, “upper”,“lower”, etc., are used for convenience in referring to the accompanyingdrawings. In general, “above”, “upper”, “upward” and similar terms referto a direction toward the earth's surface along a wellbore, and “below”,“lower”, “downward” and similar terms refer to a direction away from theearth's surface along the wellbore.

Representatively illustrated in FIG. 1 is a well system 10 andassociated method which embody principles of the present invention. Atubular string 12 is installed in a wellbore 14 lined with casing 16.Suspended from the tubular string 12 is a perforating assembly 18 whichis used to form perforations 20 through the casing 16, through cement 22surrounding the casing, and into one or more subterranean formations orzones 24.

Although the perforating assembly 18 is depicted in FIG. 1 as being ofthe type known to those skilled in the art as a “tubing conveyed”perforating assembly, other types of perforating assemblies may be usedin keeping with the principles of the invention. For example, theperforating assembly 18 could be conveyed by wireline, slickline or anyother form of conveyance.

Furthermore, although the perforating assembly 18 is used as an exampleof an assembly which utilizes explosive components, other types ofassemblies may be used in keeping with the principles of the invention.For example, casing cutters, setting tools and other types of well toolsand equipment are known which include explosive components, and whichcan benefit from the principles of the present invention to enhance thesafety of their operation.

Therefore, it should be clearly understood that the invention is notlimited in any manner to the specific well systems, methods, explosivessafety systems, etc. described herein. Instead, the principles of theinvention are applicable to a wide variety of well tools, equipment andoperations which utilize explosive components.

The perforating assembly 18 depicted in FIG. 1 includes a firing head 26for initiating detonation of explosive perforating charges (not visiblein FIG. 1) of perforating guns 28. The firing head 26 may be actuated inany manner to initiate detonation of the perforating charges. Forexample, pressure, telemetry (such as acoustic, pressure pulse,electromagnetic or other form of telemetry), mechanical force,electrical signal, or other stimulus may be used.

Although one firing head 26 above the perforating guns 28 is illustratedin FIG. 1, there may be multiple firing heads, a firing head may beattached at a lower end of the perforating assembly 18 below theperforating guns, and different types of firing heads may be used, inkeeping with the principles of the invention.

In an important feature of the well system 10, the perforating assembly18 also includes thermally activated explosives safety systems 30, 32.The safety system 30 is depicted in FIG. 1 as being interconnectedbetween the firing head 26 and the upper perforating gun 28, in order toprevent the firing head from undesirably initiating detonation of theperforating guns, and the safety system 32 is depicted in FIG. 1 asbeing interconnected between the perforating guns, in order to preventundesirable transfer of detonation between the perforating guns.

However, it should be clearly understood that these positions of thesafety systems 30, 32 are merely examples of a variety of differentpositions in which the safety systems can have beneficial use. Forexample, it is known practice to include a shearable safety joint in aperforating assembly to allow safer connection and disconnection of afiring head while the safety joint is positioned in a blowout preventerstack.

An example of such a shearable safety joint is described in U.S. Pat.No. 6,675,896, the entire disclosure of which is incorporated herein bythis reference. An explosives safety system (such as one of the safetysystems 30, 32) could be interconnected between the safety joint and theperforating guns, or incorporated as part of the safety joint, tothereby provide an increased measure of safety while the firing head isbeing connected or disconnected.

Referring additionally now to FIG. 2, a schematic cross-sectional viewof a thermally activated explosives safety system 40 is representativelyillustrated. The safety system 40 may be used for the safety systems 30,32 in the well system 10 of FIG. 1. The safety system 40 may also beused in other well systems in keeping with the principles of theinvention.

As depicted in FIG. 2, the safety system 40 includes an assembly 42positioned between a firing pin 44 and an explosive component. Thedetails of the assembly 42 are not visible in FIG. 2, but examples ofthe assembly will be described in detail below.

The assembly 42 selectively prevents the firing pin 44 from contactingthe explosive component 46 to thereby prevent detonation of theexplosive component. The assembly 42 may prevent such contact betweenthe firing pin 44 and the explosive component 46 in various ways, forexample, by blocking a passage 48 between the firing pin and theexplosive component. The assembly 42 may prevent contact between thefiring pin 44 and the explosive component 46 in any manner (some ofwhich are described in detail below) in keeping with the principles ofthe invention.

The firing pin 44 may be a part of the firing head 26, or it may be partof another portion of the perforating assembly 18 (such as a detonationtransfer sub). The firing pin 44 may be displaced in response to anytype of stimulus, such as mechanical force, pressure, detonation ofanother explosive component adjacent the firing pin, etc.

The explosive component 46 is depicted in FIG. 2 as being of the typeknown to those skilled in the art as an initiator. Detonation of theinitiator is transferred to another explosive component 50 of the typeknown to those skilled in the art as a booster, and detonation of thebooster is transferred to yet another explosive component 52 of the typeknown to those skilled in the art as a detonating cord.

The explosive components 46, 50, 52 described above are merely examplesof the wide variety of explosive components for which detonation may beselectively permitted and prevented using the safety system 40. Othertypes include, but are not limited to, perforating charges, cuttingcharges, strip charges, linear charges, setting charges, etc.

Referring additionally now to FIG. 3, an alternate configuration of thesafety system 40 is representatively illustrated. In this configuration,the assembly 42 is used to selectively permit and prevent transfer ofdetonation between multiple boosters (explosive components 50) connectedto multiple lengths of detonating cord (explosive components 52).

The assembly 42 may prevent such detonation transfer by, for example,blocking the passage 48 between the explosive components 50. However,the assembly 42 may prevent detonation transfer between the explosivecomponents 50 in any manner (some of which are described in detailbelow) in keeping with the principles of the invention.

Referring additionally now to FIG. 4, a schematic cross-sectional viewof the safety system 40 is representatively illustrated. In this view itmay be seen that this configuration of the assembly 42 includes ablocking member 54 in the form of a plate which blocks the passage 48 toprevent detonation of an explosive component (for example, by preventingcontact between the firing pin 44 and the explosive component 46, bypreventing detonation transfer between the explosive components 50,etc.).

The assembly 42 further includes a thermal actuator 56 for displacingthe blocking member 54 relative to the passage 48. The thermal actuator56 is preferably of the type which includes a material having a volumewhich varies in response to temperature change.

Suitable thermal actuators are manufactured by Therm-Omega-Tech, Inc.(which actuators include a material that changes phase at apredetermined temperature), Caltherm Corporation, Rostra Vernatherm LLC,and others. Thermal actuators are available which extend or lengthenupon a temperature increase and retract upon a temperature decrease,which retract upon a temperature increase and extend or lengthen upon atemperature decrease, and others which rotate in response to atemperature change.

As depicted in FIG. 4, the thermal actuator 56 is of the type whichextends upon a temperature increase, but the actuator is shown in itsretraced configuration. A rod 58 of the actuator 56 is connected to theblocking member 54.

The actuator 56 may be assisted in maintaining the blocking member 54 inits position blocking the passage 48 by means of biasing devices 60(such as springs, etc.). Alternatively, the actuator 56 may be capableof exerting sufficient force to displace the member 54 to this position,and to maintain the member in this position, without use of the biasingdevices 60.

Referring additionally now to FIG. 5, the safety system 40 isrepresentatively illustrated after a temperature increase has caused theactuator 56 to extend the rod 58 further outward and thereby displacethe blocking member 54 so that it no longer blocks the passage 48.Detonation of the explosive components 46, 50, 52 in either of theconfigurations of FIGS. 2 & 3 is now permitted by the safety system 40.

The temperature increase is preferably due to installation of the safetysystem 40 in the well. Of course, the local geothermal gradient and thedepth at which the safety system 40 is to be installed are factors whichwill influence the available temperature increase and, thus, the designof the thermal actuator 56, so that reliable operation of the assembly42 in a particular well system is assured.

In an important feature of the safety system 40, the displacement of theblocking member 54 by the thermal actuator 56 is reversible, and may bereversible multiple times. That is, the thermal actuator 56 may displacethe blocking member 54 to its positions depicted in FIGS. 4 & 5 inresponse to any number of respective temperature increases anddecreases.

For example, when used in the well system 10 of FIG. 1, the safetysystem 40 may be used to prevent detonation of the explosive components46, 50, 52 while the perforating assembly 18 is near the surface (i.e.,at a relatively low temperature). When the perforating assembly 18(including the safety system 40) is installed in the wellbore 14, theresulting temperature increase will cause the actuator 56 to displacethe blocking member 54, so that detonation of the explosive components46, 50, 52 is permitted (as depicted in FIG. 5). Upon retrieval of theperforating assembly 18 to the surface (such as due to a misfire of thefiring head 26, or another circumstance resulting in undetonatedexplosive components possibly being brought back to the surface), theresulting temperature decrease will cause the actuator 56 to displacethe blocking member 54 back to its position blocking the passage 48 andpreventing detonation of the explosive components 46, 50, 52.

Referring additionally now to FIGS. 6 & 7, schematic cross-sectionalviews of an alternate configuration of the safety system 40 arerepresentatively illustrated. In this configuration, the blocking member54 is pivoted or rotated about a pivot 62 by the actuator 56, instead ofbeing displaced laterally relative to the passage 48 as in theconfiguration of FIGS. 4 & 5.

In FIG. 6, the member 54 blocks the passage 48, and detonation of theexplosive components 46, 50, 52 is thereby prevented at a correspondingrelatively low temperature. In FIG. 7, the member 54 does not block thepassage 48, and detonation of the explosive components 46, 50, 52 isthereby permitted at a corresponding relatively high temperature.

As with the configuration of FIGS. 4 & 5 (and the other alternateconfigurations of the safety system 40 described below), thedisplacement of the blocking member 54 is reversible. Thus, the safetysystem 40 always prevents detonation of the explosive components 46, 50,52 at any time the safety system is at a sufficiently low temperature(such as near the surface or at a depth relatively shallow in the well).

Referring additionally now to FIG. 8, a schematic cross-sectional viewof another alternate configuration of the safety system 40 isrepresentatively illustrated. In this configuration, the blocking member54 is displaced laterally by the actuator 56 in a recess 64 whichintersects the passage 48.

The blocking member 54 has an opening 66 formed therein which may bealigned with the passage 48 when it is desired to permit detonation ofthe explosive components 46, 50, 52. As depicted in FIG. 8, the member54 is in a position in which the opening 66 is not aligned with thepassage 48, and so detonation of the explosive components 46, 50, 52 isprevented. The actuator 56 will displace the member 54 to align theopening 66 and passage 48 in response to a sufficient increase intemperature.

In the configuration as shown in FIG. 8, the firing pin 44 is propelledthrough the passage 48 in response to detonation of a detonating cord(explosive component 52) and booster (explosive component 50) above thefiring pin. Until such detonation occurs, the firing pin 44 is securedin place by shear pins 68 or other suitable fasteners. A vent passage 70prevents undesirable pressure increase in the passage 48 below thefiring pin 44 when the firing pin is propelled downward through thepassage.

Referring additionally now to FIG. 9, a schematic cross-sectional viewof another alternate configuration of the safety system 40 isrepresentatively illustrated. This configuration is similar in manyrespects to the configuration of FIG. 8.

However, in this configuration the blocking member 54 does not includethe opening 66. Instead, the blocking member 54 is displaced by theactuator 56 to a position in which it no longer blocks the passage 48 inresponse to a sufficient temperature increase.

For this purpose, the actuator 56 is of the type in which the rod 58 isretracted (to thereby laterally displace the member 54 so that it nolonger blocks the passage 48) in response to a temperature increase. Theactuator 56 will extend the rod 58 (to thereby laterally displace themember 54 so that it again blocks the passage 48) in response to asubsequent temperature decrease.

Thus, the actuator 56 is preferably of the type which is known to thoseskilled in the art as a “reverse” thermal actuator. Such actuators stillinclude a material having a volume which varies in response to atemperature change, but the actuators are constructed in a mannercausing the actuators to lengthen or extend in response to a temperaturedecrease, and causing the actuators to retract in response to atemperature increase.

As will be readily appreciated from the above descriptions of variousconfigurations of the safety system 40, detonation of an explosivecomponent may be prevented by blocking a passage (for example, to blockdisplacement of a firing pin through the passage, or to preventdetonation transfer between explosive components, etc.), and detonationof the explosive component may be permitted by unblocking the passage.Referring additionally now to FIGS. 10 & 11, schematic cross-sectionalviews of another alternate configuration of the safety system 40 isrepresentatively illustrated, in which another manner of blocking andunblocking the passage 48 may be accomplished.

In this configuration, the blocking member 54 is in the form of a shaftwhich is rotated in the recess 64 intersecting the passage 48. Thisrotation of the shaft is caused by the actuator 56 which extends orretracts the rod 58 in response to corresponding increases or decreasesin temperature.

The rod 58 is connected to the blocking member 54 by means of a yoke 72and arm 74. The yoke 72 and arm 74 transfer linear displacement of therod 58 into rotational displacement of the blocking member 54.

As depicted in FIG. 10, the opening 66 is rotated so that it is notaligned with the passage 48, and the passage is thus blocked, preventingdetonation of the explosive components 46, 50, 52. As depicted in FIG.11, the opening is rotated so that it is aligned with the passage 48,and the passage is thus unblocked, permitting detonation of theexplosive components 46, 50, 52.

The blocking member 54 is rotated to the position shown in FIG. 10 inresponse to a temperature decrease, and the blocking member is rotatedto the position shown in FIG. 11 in response to a temperature increase.As with the other configurations of the safety system 40 describedherein, these displacements of the blocking member 54 are reversible andrepeatable.

Note that, in the configuration of FIGS. 10 & 11, the blocking member 54is rotated about an axis (defined by the recess 64) which is orthogonalto the passage 48. In contrast, in the configuration of FIGS. 6 & 7, theblocking member 54 is rotated about an axis (defined by the pivot 62)which is parallel to the passage 48.

In some embodiments of the safety system 40, greater displacement may bedesired than can conveniently be obtained from a single thermal actuator56. In those circumstances, multiple thermal actuators 56 may be used,with the actuators being connected in series.

Similarly, in some embodiments of the safety system 40, greater forcemay be desired than can conveniently be obtained from a single thermalactuator 56. In those circumstances, multiple thermal actuators 56 maybe used, with the actuators being connected in parallel.

In FIGS. 12 & 13, an example is representatively illustrated of multipleactuators 56 connected in series. Although only two actuators 56 aredepicted, any number of actuators may be connected in series (and/or inparallel).

In FIG. 12, the actuators 56 are in their retracted configurations. InFIG. 13, the actuators 56 are in their extended configurations. It willbe readily appreciated that the actuators 56 connected in series canproduce greater displacement than a single one of the actuators canproduce.

Referring additionally now to FIG. 14, a schematic cross-sectional viewof another alternate configuration of the safety system 40 isrepresentatively illustrated. In this configuration, multiple actuators56 are used to produce sufficient displacement to rotate the blockingmember 54 relative to the passage 48.

In addition, the displacement produced by the actuators 56 istransmitted to the arm 74 connected to the blocking member 54 via a rod76, and the yoke 72 is integrally formed with the arm 74. The biasingdevice 60 biases the rod 76 downward, i.e., so that the blocking member54 is rotated to its position blocking the passage 48 when the actuators56 are in their retracted configurations. As discussed above, thebiasing device 60 may not be used if the actuators 56 produce sufficientretracting force to rotate the blocking member 54 without assistancefrom the biasing device.

Referring additionally now to FIG. 15, a schematic cross-sectional viewof another alternate configuration of the safety system 40 isrepresentatively illustrated. In this configuration, the safety system40 does not selectively block and unblock the passage 48 to therebyrespectively prevent and permit detonation of the explosive components46, 50, 52.

Instead, additional explosive components 50, 52 contained in a shuttle80 are displaced by a material 78 having a volume which varies inresponse to changes in temperature. This material 78 may be the same asthe material used in the actuators 56 described above.

The material 78 may be a solid, a liquid, a gas, a gel, a plastic, acombination thereof, or any other type of material. The material 78 maychange phase to produce relatively large changes in volume.

For example, a material known as THERMOLOID™ is used in the thermalactuators available from Therm-Omega-Tech, Inc. This material (as wellas other materials) may be suitable for use as the material 78 in thesafety system 40 of FIG. 15. Indeed, the combination of the shuttle 80and the material 78 in a chamber 82 of the assembly 42 may be consideredas the thermal actuator 56 in this embodiment of the safety system 40.

The material 78 increases in volume in response to a temperatureincrease. When the material 78 increases in volume, the shuttle 80 isdisplaced laterally relative to the passage 48. Eventually, theexplosive components 50, 52 contained in the shuttle 80 are aligned withthe explosive components 50 in the passage 48, and detonation transferthrough the passage is permitted.

The biasing device 60 biases the shuttle 80 toward the chamber 82 sothat, when the temperature decreases and the volume of the material 78correspondingly decreases, the shuttle will displace laterally and theexplosive components 50, 52 in the shuttle will no longer be alignedwith the explosive components in the passage 48. Detonation transferthrough the passage 48 will thereby be prevented.

Other types of thermal actuators, such as the thermal actuators 56described above and depicted in FIGS. 2-14, may be used in place of thematerial 78 in the chamber 82 to displace the shuttle 80, if desired.

Referring additionally now to FIGS. 16 & 17, schematic cross-sectionalviews of another alternate configuration of the safety system 40 arerepresentatively illustrated. In this configuration, the thermalactuator 56 includes an arm 84 made of a material which changes shape inresponse to changes in temperature.

The arm 84 is connected to the blocking member 54. At relatively lowtemperature, the arm 84 has a shape which positions the blocking member54 so that it blocks the passage 48, thereby preventing detonation ofexplosive components 50, 52 on one side of the member, as depicted inFIG. 16.

However, at a relatively high temperature, the arm 84 has another shapewhich positions the blocking member 54 so that it does not block thepassage 48, thereby permitting detonation of the explosive components50, 52 on either side of the recess 64, as depicted in FIG. 17.

The arm 84 could be constructed of various different materials. Examplesof suitable materials include, but are not limited to, bimetallics,shape memory alloys, etc.

Referring additionally now to FIG. 18, a schematic cross-sectional viewof another alternate configuration of the safety system 40 isrepresentatively illustrated. In this configuration, the assembly 42includes the variable volume material 78 contained within an enclosure86 positioned between a rod 88 and the firing pin 44 in the passage 48.

The rod 88 is propelled downward in response to detonation of explosivecomponents 50, 52 above a piston 90 at an upper end of the rod. Theenclosure 86 is preferably somewhat flexible, so that if the material 78is at a relatively low temperature (and the material thus has a reducedvolume), insufficient force will be transmitted from the rod 88 to thefiring pin 44 to shear the shear pin 68 retaining the firing pin in theposition shown in FIG. 18.

However, when the material 78 is at a relatively high temperature, theincrease in volume of the material causes the combined material andenclosure 86 in the assembly 42 to become more rigid. In this condition,the material 78 and enclosure 86 in the assembly 42 can transmitsufficient force from the rod 88 to the firing pin 44 to shear the shearpins 68 and propel the firing pin into contact with the explosivecomponent 46, thereby detonating the explosive components 46, 50, 52.

Referring additionally now to FIG. 19, a schematic cross-sectional viewof another alternate configuration of the safety system 40 isrepresentatively illustrated. This configuration is similar in manyrespects to the configuration of FIG. 18. However, the rod 88, piston 90and associated biasing device 60 and shear pins 68 are not used in theconfiguration of FIG. 19.

Instead, detonation of the explosive components 50, 52 above theassembly 42 (which includes the material 78 and the enclosure 86)applies a downwardly directed force to the assembly. If the material 78is at a relatively high temperature (and thus has an increased volume),then the assembly 42 will have increased rigidity and sufficient forcewill be transmitted through the assembly to the firing pin 44 to propelthe firing pin into contact with the explosive component 46. If,however, the material 78 is at a relatively low temperature (and thushas a reduced volume), then the assembly 42 will have a correspondinglyreduced rigidity and sufficient force will not be transmitted throughthe assembly to the firing pin 44 to cause detonation of the explosivecomponent 46.

In the configurations of FIGS. 18 & 19, the enclosure 86 may be made ofany material suitable to contain the material 78 when it has increasedvolume, and to withstand the resulting stress caused by the expansion ofthe material 78, while being sufficiently flexible to reduce forcetransmission through the assembly 42 when the material 78 has a reducedvolume. For example, the enclosure 86 could be made of high strengthpolymers, relatively thin metals, etc.

Referring additionally now to FIG. 20, a schematic cross-sectional viewof another alternate configuration of the safety system 40 isrepresentatively illustrated. In this configuration, the actuator 56 isused to extend and retract the firing pin 44 in response tocorresponding increases and decreases in temperature of the material 78in the actuator.

In contrast to the other embodiments of the safety system 40 describedabove, the firing pin 44 is a part of the actuator 56 in theconfiguration of FIG. 20. For example, the firing pin 44 may be formedon an end of the rod 58.

When a sufficient force 92 is applied to the upper end of the actuator56, shear pins 68 will shear and the actuator will be propelled downwardthrough the passage 48 toward the explosive component 46. The force 92may be applied mechanically, by pressure, such as detonation ofexplosive components above the actuator 56, or by other means.

If the firing pin 44 extends outwardly from the actuator 56 a sufficientdistance, then the firing pin will contact the explosive component 46and cause detonation of the explosive components 46, 50, 52. If,however, the firing pin 44 is retracted into the actuator 56 (asdepicted in FIG. 20), then the firing pin will not contact the explosivecomponent 46.

The firing pin 44 extends outwardly from the actuator 56 in response toa temperature increase, which causes the volume of the material 78 toincrease. A piston 94 at an upper end of the rod 58 is displaceddownward when the material 78 volume increases, thereby downwardlydisplacing and outwardly extending the firing pin.

Similarly, the firing pin 44 is retracted when the material 78 is at arelatively low temperature and has a corresponding reduced volume. Thebiasing device 60 may assist in upwardly displacing the piston 94, rod58 and firing pin 44 if the decreased volume of the material 78 does notproduce sufficient force to do this without the aid of the biasingdevice.

Referring additionally now to FIG. 21, a schematic cross-sectional viewof another alternate configuration of the safety system 40 isrepresentatively illustrated. In this configuration, the actuator 56 isused to alternately increase and decrease a gap G between the actuatorand explosive components 50, 52 above the actuator.

When the gap G is sufficiently large, detonation of the explosivecomponents 50, 52 above the actuator 56 will not generate sufficientdownward force on the actuator to cause the shear pins 68 to shear andpropel the firing pin 44 into contact with the explosive component 46.However, when the gap G is sufficiently small, the force applied to theactuator 56 will be great enough to cause the shear pins 68 to shear andpropel the firing pin 44 into contact with the explosive component 46,thereby causing detonation of the explosive components 46, 50, 52.

The size of the gap G is determined by the volume of the material 78,which is positioned between a piston 96 connected to the firing pin 44and an outer housing 98 of the actuator 56. When the material 78 volumeincreases in response to increased temperature, the housing 98 isdisplaced upward, thereby reducing the gap G.

When the material 78 volume decreases in response to reducedtemperature, the housing 98 is displaced downward, thereby increasingthe gap G. The biasing device 60 may assist in displacing the housing 98downward, if desired.

Referring additionally now to FIG. 22, a schematic cross-sectional viewof another alternate configuration of the safety system 40 isrepresentatively illustrated. In this configuration, the thermalactuator 56 is used to rotate the blocking member 54 relative to thepassage 48.

The blocking member 54 rotates about a pivot 100. The pivot 100 definesan axis of rotation of the blocking member 54 which is orthogonal to thepassage 48.

As depicted in FIG. 22, the actuator 56 has rotated the blocking member54 to a position in which the passage 48 is unblocked, and so detonationof the explosive components 46, 50, 52 below the assembly 42 ispermitted. The actuator 56 rotates the blocking member 54 to thisposition in response to increased temperature.

However, when the temperature is sufficiently low, the actuator 56 willrotate the blocking member 54 (clockwise as viewed in FIG. 22) to aposition in which the member blocks the passage 48 and detonation of theexplosive components 46, 50, 52 below the assembly 42 is prevented.

Referring additionally now to FIG. 23, a schematic cross-sectional viewof another alternate configuration of the safety system 40 isrepresentatively illustrated. In this configuration, the blocking member54 is displaced laterally by the actuator 56 in the recess 64 whichintersects the passage 48.

The blocking member 54 has the opening 66 formed therein which may bealigned with the passage 48 when it is desired to permit detonation ofthe explosive components 46, 50, 52 below the assembly 42. As depictedin FIG. 23, the member 54 is in a position in which the opening 66 isnot aligned with the passage 48, and so detonation of the explosivecomponents 46, 50, 52 below the assembly 42 is prevented. The actuator56 will displace the member 54 to align the opening 66 and passage 48 inresponse to a sufficient increase in temperature.

The member 54 is displaced laterally in response to extension andretraction of the rod 58 by the actuator 56. Specifically, a rounded endof the rod 58 engages a rounded end of the member 54 to thereby causelateral displacement of the member, similar to a cam and followerarrangement.

In the configuration as shown in FIG. 23, the firing pin 44 is propelledthrough the passage 48 in response to detonation of the detonating cord(explosive component 52) and booster (explosive component 50) above thefiring pin. Until such detonation occurs, the firing pin 44 is securedin place by the shear pins 68 or other suitable fasteners.

Referring additionally now to FIG. 24, a schematic cross-sectional viewof another alternate configuration of the safety system 40 isrepresentatively illustrated. In this configuration, the actuator 56 rod58 engages a recess 102 formed in the firing pin 44 to thereby preventdetonation of the explosive components 46, 50, 52 below the assembly 42.

When the temperature is increased sufficiently, the actuator 56 willretract the rod 58 from the recess 102, thereby permitting the firingpin 44 to be propelled downward through the passage 48 in response todetonation of the explosive components 50, 52 above the firing pin.However, when the actuator 56 is at a relatively low temperature,engagement between the rod 58 and the recess 102 prevents displacementof the firing pin 44, even though detonation of the explosive components50, 52 above the firing pin might produce sufficient force to shear theshear pins 68.

It may now be fully appreciated that the various configurations of thethermally activated explosives safety system 40 described above providegreatly improved safety in well operations utilizing explosivecomponents.

Although some of the configurations of the safety system 40 have beendescribed above as if the configuration is used to selectively permitand prevent detonation transfer between explosive components, and otherconfigurations of the safety system have been described above as if theconfiguration is used to selectively permit and prevent contact betweena firing pin and an explosive component, it should be clearly understoodthat any of the configurations may be used for either purpose withappropriate modifications.

For convenience and clarity of description, the various configurationsof the safety system 40 have been described above with eachconfiguration oriented as if detonation transfer occurs in a downwarddirection through the safety system. It will be appreciated, however,that detonation transfer can occur in an upward direction (for example,if a firing head initiates detonation from the bottom of a perforatingassembly, etc.) or horizontally, or at any inclination. Accordingly, itshould be understood that the various configurations of the safetysystem 40 may be used in any orientation in keeping with the principlesof the invention.

Of course, a person skilled in the art would, upon a carefulconsideration of the above description of representative embodiments ofthe invention, readily appreciate that many modifications, additions,substitutions, deletions, and other changes may be made to thesespecific embodiments, and such changes are within the scope of theprinciples of the present invention. Accordingly, the foregoing detaileddescription is to be clearly understood as being given by way ofillustration and example only, the spirit and scope of the presentinvention being limited solely by the appended claims and theirequivalents.

1. A thermally activated explosives safety system, comprising: anexplosive component; a blocking member displaceable to selectivelypermit and prevent detonation of the explosive component; and a thermalactuator responsive to temperature change, the actuator being configuredto displace the blocking member in response to the temperature change.2. The system of claim 1, wherein the actuator includes a material, avolume of the material being variable in response to the temperaturechange.
 3. The system of claim 2, wherein the material volume increasesin response to a temperature increase, and wherein the material volumedecreases in response to a temperature decrease.
 4. The system of claim2, wherein the blocking member displaces to a position preventingdetonation of the explosive component in response to an increase in thematerial volume.
 5. The system of claim 2, wherein the blocking memberdisplaces to a position permitting detonation of the explosive componentin response to an increase in the material volume.
 6. The system ofclaim 1, wherein the actuator displaces the blocking member to aposition preventing detonation of the explosive component in response toa temperature decrease.
 7. The system of claim 1, wherein the actuatordisplaces the blocking member to a position permitting detonation of theexplosive component in response to a temperature increase.
 8. The systemof claim 1, wherein the blocking member is positioned between a firinghead and a perforating gun.
 9. The system of claim 1, wherein theblocking member is positioned between perforating guns.
 10. The systemof claim 1, wherein the blocking member is positioned between a firingpin and the explosive component.
 11. The system of claim 1, wherein thesystem includes at least two explosive components, and wherein theblocking member is positioned between the explosive components.
 12. Thesystem of claim 1, wherein the blocking member is displaced laterallyrelative to a passage by the actuator in response to the temperaturechange.
 13. The system of claim 1, wherein the blocking member isrotated by the actuator about an axis parallel to a passage in responseto the temperature change.
 14. The system of claim 1, wherein theblocking member is rotated by the actuator about an axis orthogonal to apassage in response to the temperature change.
 15. The system of claim1, wherein the blocking member blocks a passage to prevent detonation ofthe explosive component.
 16. The system of claim 1, wherein the blockingmember has an opening which is aligned with a passage to permitdetonation of the explosive component.
 17. The system of claim 1,further comprising a biasing device which biases the blocking member ina direction to prevent detonation of the explosive component.
 18. Thesystem of claim 1, wherein the system includes at least two of thethermal actuators, and wherein the actuators are cooperatively operableto displace the blocking member.
 19. The system of claim 1, wherein theactuator includes a bimetallic structure which changes shape in responseto the temperature change.
 20. The system of claim 1, wherein theactuator includes a shape memory alloy material which changes shape inresponse to the temperature change.
 21. The system of claim 1, whereinthe blocking member engages a firing pin to prevent displacement of thefiring pin and thereby prevent detonation of the explosive component.22. A thermally activated explosives safety system, comprising: anexplosive component; a thermal actuator responsive to temperaturechange, the actuator including a material having a volume which isvariable in response to the temperature change; and wherein detonationof the explosive component is selectively permitted and prevented by theactuator when the material volume changes.
 23. The system of claim 22,wherein detonation of the explosive component is prevented when thematerial volume increases.
 24. The system of claim 22, whereindetonation of the explosive component is prevented when the materialvolume decreases.
 25. The system of claim 22, wherein the materialvolume increases in response to a temperature increase, and wherein thematerial volume decreases in response to a temperature decrease.
 26. Thesystem of claim 22, wherein a blocking member displaces to a positionpreventing detonation of the explosive component in response to anincrease in the material volume.
 27. The system of claim 22, wherein ablocking member displaces to a position permitting detonation of theexplosive component in response to an increase in the material volume.28. The system of claim 22, wherein the actuator displaces a blockingmember to a position preventing detonation of the explosive component inresponse to a temperature decrease.
 29. The system of claim 22, whereinthe actuator displaces a blocking member to a position permittingdetonation of the explosive component in response to a temperatureincrease.
 30. The system of claim 22, wherein a blocking memberdisplaceable by the actuator blocks a passage to prevent detonation ofthe explosive component.
 31. The system of claim 22, wherein theactuator includes a bimetallic structure which changes shape in responseto the temperature change.
 32. The system of claim 22, wherein theactuator includes a shape memory alloy material which changes shape inresponse to the temperature change.
 33. The system of claim 22, whereinthe actuator reduces a gap between elements of the system to therebypermit detonation of the explosive component.
 34. The system of claim22, wherein the actuator extends a firing pin outwardly to therebypermit detonation of the explosive component.
 35. The system of claim22, wherein the actuator aligns multiple elements of an explosive trainto thereby permit detonation of the explosive component.
 36. The systemof claim 22, wherein the actuator displaces a blocking member to therebypermit detonation of the explosive component.
 37. The system of claim22, wherein the actuator aligns an opening with a passage to therebypermit detonation of the explosive component.
 38. The system of claim22, wherein the actuator rotates a blocking member to thereby permitdetonation of the explosive component.
 39. A method of preventingundesired detonation of an explosive component, the method comprisingthe steps of: providing a material having a volume which is variable inresponse to a change in a temperature of the material; positioning thematerial and the explosive component in a subterranean well, therebyincreasing the temperature of the material; increasing the volume of thematerial in response to the temperature increasing step; and permittingdetonation of the explosive component in response to the volumeincreasing step.
 40. The method of claim 39, further comprising thesteps of decreasing the volume of the material in response to decreasingthe temperature of the material, and preventing detonation of theexplosive component in response to the volume decreasing step.
 41. Themethod of claim 40, wherein the volume decreasing and detonationpreventing steps are performed after the volume increasing anddetonation permitting steps.
 42. The method of claim 39, furthercomprising the step of preventing detonation of the explosive component,and wherein the detonation preventing step is performed prior to thevolume increasing and detonation permitting steps.
 43. The method ofclaim 39, further comprising the step of containing the material in anenclosure, thereby forming an assembly which becomes increasingly rigidas the volume of the material increases.
 44. The method of claim 43,further comprising the step of transmitting a force through the assemblywhen the assembly has an increased rigidity to thereby detonate theexplosive component.
 45. The method of claim 43, further comprising thestep of preventing detonation of the explosive component by preventingeffective transmission of a force through the assembly when the assemblyhas a reduced rigidity.
 46. The method of claim 39, wherein theproviding step further comprises providing the material as part of athermal actuator.
 47. The method of claim 46, wherein the detonationpermitting step further comprises the actuator displacing a blockingmember in response to the volume increasing step.
 48. The method ofclaim 46, wherein the detonation permitting step further comprises theactuator rotating a blocking member in response to the volume increasingstep.
 49. The method of claim 46, wherein the detonation permitting stepfurther comprises the actuator extending a firing pin outward inresponse to the volume increasing step.
 50. The method of claim 46,wherein the detonation permitting step further comprises the actuatordecreasing a gap in response to the volume increasing step.
 51. Themethod of claim 46, wherein the detonation permitting step furthercomprises the actuator aligning multiple explosive components inresponse to the volume increasing step.